An experimental MOSFET approach to characterize (192)Ir HDR source anisotropy

• Published in: Physics in medicine & biology Vol. 52; no. 17; p. 5329
• Main Authors: Toye, W C, Das, K R, Todd, S P, Kenny, M B, Franich, R D, Johnston, P N
• Format: Journal Article
• Language: English
• Published: England 07-09-2007
• Subjects: Anisotropy; Brachytherapy - methods; Equipment Design; Equipment Failure Analysis; Iridium Radioisotopes - analysis; Iridium Radioisotopes - chemistry; Radiometry - instrumentation; Radiometry - methods; Radiotherapy Dosage; Reproducibility of Results; Scattering, Radiation; Sensitivity and Specificity; Transistors, Electronic
• ISSN: 0031-9155
• DOI: 10.1088/0031-9155/52/17/015

The dose anisotropy around a (192)Ir HDR source in a water phantom has been measured using MOSFETs as relative dosimeters. In addition, modeling using the EGSnrc code has been performed to provide a complete dose distribution consistent with the MOSFET measurements. Doses around the Nucletron 'classic' (192)Ir HDR source were measured for a range of radial distances from 5 to 30 mm within a 40 x 30 x 30 cm(3) water phantom, using a TN-RD-50 MOSFET dosimetry system with an active area of 0.2 mm by 0.2 mm. For each successive measurement a linear stepper capable of movement in intervals of 0.0125 mm re-positioned the MOSFET at the required radial distance, while a rotational stepper enabled angular displacement of the source at intervals of 0.9 degrees . The source-dosimeter arrangement within the water phantom was modeled using the standardized cylindrical geometry of the DOSRZnrc user code. In general, the measured relative anisotropy at each radial distance from 5 mm to 30 mm is in good agreement with the EGSnrc simulations, benchmark Monte Carlo simulation and TLD measurements where they exist. The experimental approach employing a MOSFET detection system of small size, high spatial resolution and fast read out capability allowed a practical approach to the determination of dose anisotropy around a HDR source.